Question: $ D = \left[\begin{array}{rrr}0 & 1 & 2 \\ 1 & 1 & 1 \\ 2 & 1 & 1\end{array}\right]$ What is $ D^{-1}$ ?
$ = \left[\begin{array}{rrr}0 & -1 & 1 \\ -1 & 4 & -2 \\ 1 & -2 & 1\end{array}\right]$